Drug Interactions between Bethaprim Pediatric and Capozide

MONITOR CLOSELY: The use of trimethoprim in combination with other potassium-sparing drugs or potassium salts may increase the risk of hyperkalemia. Trimethoprim inhibits sodium reabsorption and potassium excretion by blocking sodium channels in the renal distal tubules. Studies of patients treated with standard and high dosages of trimethoprim-sulfamethoxazole compared to similar controls treated with other antibiotics indicate that reversible increases in serum potassium are fairly common with trimethoprim use. Although generally asymptomatic, severe hyperkalemia including metabolic acidosis, paralysis, nonoliguric renal failure, and ventricular arrhythmia have been reported. Risk factors for developing hyperkalemia include use of high dosages of trimethoprim (e.g., for the treatment of MRSA skin infections or Pneumocystis jiroveci pneumonia (PCP) in AIDS patients); renal impairment or age-related decline in renal function; aldosterone or adrenal insufficiency; concomitant use of drugs that increase the risk of hyperkalemia (e.g., ACE inhibitors, angiotensin II receptor blockers, aldosterone antagonists; potassium-sparing diuretics); diets with potassium-rich foods (e.g., tomatoes, raisins, figs, baked potatoes, bananas, papayas, pears, cantaloupe, mangoes); and use of potassium salt substitutes.

MANAGEMENT: Serum potassium and sodium levels as well as renal function should be closely monitored during coadministration of trimethoprim with other potassium-sparing drugs or potassium salts, particularly in patients receiving high-dose or long-term trimethoprim treatment and in patients with renal impairment, diabetes, old age, severe or worsening heart failure, or dehydration. A dosage reduction of trimethoprim is recommended in renal dysfunction (50% reduction for CrCl between 15 and 30 mL/min). Patients should be given dietary counseling to avoid excessive intake of potassium-rich foods and salt substitutes, and advised to seek medical attention if they experience signs and symptoms of hyperkalemia such as nausea, vomiting, weakness, listlessness, tingling of the extremities, paralysis, confusion, weak pulse, and a slow or irregular heartbeat. Trimethoprim should be discontinued if hyperkalemia occurs.

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MONITOR: Although they are frequently combined in clinical practice, diuretics and angiotensin converting enzyme (ACE) inhibitors may have additive effects. Coadministration makes hypotension and hypovolemia more likely than does either drug alone. Some ACE inhibitors may attenuate the increase in the urinary excretion of sodium caused by some loop diuretics. Some patients on diuretics, especially those on dialysis or a dietary salt restriction, may experience acute hypotension with lightheadedness and dizziness after receiving the first dose of the ACE inhibitor. In addition, ACE inhibitors may cause renal insufficiency or acute renal failure in patients with sodium depletion or renal artery stenosis.

MANAGEMENT: Monitoring of blood pressure, diuresis, electrolytes, and renal function is recommended during coadministration. The possibility of first-dose hypotensive effects may be minimized by initiating therapy with small doses of the ACE inhibitor, or either discontinuing the diuretic temporarily or increasing the salt intake approximately one week prior to initiating an ACE inhibitor. Alternatively, the patient may remain under medical supervision for at least two hours after the first dose of the ACE inhibitor, or until blood pressure has stabilized.

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